1. Field of the Invention
The present invention relates to methods, compositions, and apparatus for lysing and process algae to extract various products such as lipids, proteins, carbohydrates, metabolites. The methods involve the use of an ionic liquid (IL) to lyse harvested algae cells and using a salt as a reagent in the process and as a means of removing water from the IL after cell lysis so that the IL may be reused.
2. Description of Related Art
Algae, including microalgae, macroalgae, fresh water algae, and marine algae are potentially useful as sources of industrial, agricultural, and pharmaceutical products and their precursors.
WO 2001/060166 A1 discloses fermentation, lysis, and extraction of docosahexaenoic acid (DHA) from the marine algae Cypthecodinium cohnii and the potential use of macroalgae such as Rhodophyceae, Gigartinaceae, Gigartina stellata, and Chondrus crispus as sources of carrageenan and DHA for pet food. The non-used remains of the algae are combined with yeast in a process for making pet treats.
US 2006/0241287 A1 discloses a method for using ILs to extract and separate a biopolymer from a biomass. The biopolymer is dissolved in the IL and may then be separated from the IL. The process, and therefore the biomass, must take place in the substantial absence of water. Algae is cited in the publication as a suitable biomass source for chitin but no example of chitin extraction from algae biomass is provided and no conditions related to chitin extraction are suggested. The publication does not describe the extraction of lipids or materials other than biopolymers from biomass or the extraction of any substances from wet algae or other wet biomass.
US 2006/0141556 A1 discloses a cell lysis method using microwaves in which an ionic compound additive, which may be an IL, is used to increase the efficiency of microwave heating during a cell lysis step to prepare nucleic acid for subsequent PCR. Organic ILs such as dialkylimidazolium salts are suggested as potentially useful for the method. The amount of ionic additive used in approximately 10% by weight in the sample to be lysed and this amount is confirmed as insufficient to cause cell lysis.
US 2008/0090284 A1 discloses a system for processing oil from algae. The system comprises an algae separator, a cell lysis device, an oil separator, and a biofuel reactor. No specific means of cell lysis is suggested nor is a suggestion regarding chemical vs. mechanical lysis provided.
US 2009/0081742 discloses a method for processing algae in which steam is used to lyse algae cells. The system includes a bioreactor for synthesizing biodiesel from intracellular oil. The lysing process involves the mixture of steam with a concentrate of algae cells.
US 2009/0170184 A1 discloses a system for growing and processing algae. The system comprises bioreactors for growing algae, a dewatering unit for concentrating algae, a cell lysis chamber, and a separator for separating lysis products. Algae cells in the lysis chamber are mixed with CO2 at a pressure greater than 1 bar. Pressure/phase changes of CO2 injected into the algae cells are used to rupture the cells. The cell walls are not dissolved in the process.
US 2009/0234146 A1 discloses methods for the direct transesterification and extraction of biolipids from biomass, including plants, yeast, and algae. Large numbers of possible IL/cosolvent combinations are suggested. All examples of the process involve drying the biomass and grinding it into a fine powder.
WO 2010/023136 ('136) discloses a process for producing liquid fuels from lipid-containing biomass, including algae, by: (i) providing the biomass in a dry or semi-dry form and (ii) dissolving said the biomass in an IL at a temperature of between 60° C. and 120° C. whereby a lipid phase and a hydrophilic phase are formed. The hydrophilic phase may contain cellulose, hemi-cellulose and dissolved protein. The ILs in '136 are organic or inorganic salts having melting temperatures of about 120° C. or less and include ammonium, phosphnium, pyridinium, pyridazinium, pyramidinium, pyrazinium, imidazolium, pyrazolium, oxazolium, 1,2,3-triazolium, 1,2,4-triazolium, thiazolium, quinolium, isoquinolium, piperidinium, pyrrolidinium, and similar cations combined with anions such as halides, C1-06 carboxylates, C1-C6 alkyl sulfates, mono- and di-C1-C10 alkyl sulfosuccinates, mono- and di-C1-C10 ester sulfosuccinates, and mixtures thereof. Inorganic ILs are preferred, with ZnCl2 xH2O, x>2 most preferred, in part because biomass proteins in non-denatured (natural) form are soluble in the IL medium. For the reason, protein-containing biomass care should be taken to avoid protein denaturation.
The '136 publication discloses no examples of performing the lysis method and critical conditions for lysis such as durations of lysis and relative amounts of IL and biomass to be lysed are not suggested. Neither absolute nor relative abilities of ILs to lyse algae considered and no evidence is provided that any of the ILs are capable of lysing algae.
The aforementioned processes do not meet the need for an environmentally safe and economically viable process for producing biofuels, nutrients, and other useful products from algae biomass. Lysing algae by steam, microwaves, and mechanically induced pressure changes require relatively large amounts of energy. Chemical lysis methods often involve volatile organic chemicals or ionic detergents that interfere with subsequent separations. Drying algae to a powder requires energy for centrifugation, filtering, and/or heating. High temperatures during lysis and drying can denature proteins or degrade other desirable products. Unlike biomass obtained on land, harvested algae contains a large percentage of water. The present specification discloses methods and apparatus involving the use of certain hydrophilic ILs to lyse algae cells. The ILs and conditions disclosed are distinct from those useful for dissolving and/or processing dry biomass.
Lysis and extraction of algae cells by ILs can provide an environmentally sound alternative to more energy intensive methods, but they are expensive and have only recently been shown to lyse wet algae concentrates at temperatures as low as 80° C. U.S. Ser. No. 12/970,512, assigned to the same assignee as the present application, discloses the use of IL 1-butyl-3-methylimidazolium chloride to lyse suspensions of algae cells at temperatures of approximately 80° C. to 120° C. and to extract lipids from the resulting lysate. The lysate may also be processed to recover other materials from the algae. The IL is recovered for re-use by the addition of a salt to salt-out algal components and water.
The present invention provides methods and apparatus for processing algae at ambient temperatures using ILs, efficient recovery of IL, and recycling of salts used for IL recovery.